Without limiting the scope of the invention, its background is described in connection with drilling shales and shaly sands.
Wellbore stability is one of the most critical aspects of shale drilling and is highly dependent on the drilling fluid. Water invasion into the shale formation weakens the wellbore and causes problems such as hole collapse, stuck pipes etc. The extremely low permeability and low pore throat size of shale is such that normal filtration additives do not form mud cakes and thus do not stop fluid invasion. This research aims to reduce shale permeability by using nanoparticles (NP) to plug pore throats, build an internal and external mud cake and thereby reduce the fluid invasion into the shale.
Recent work (Osuji 2007) has shown that reducing the permeability of shale can enhance its membrane efficiency, thus it is possible that placing nanoparticles in salt-water muds could increase its membrane efficiency.
It is accepted that balanced activity oil-continuous mud (OBM) is a good solution to the shale stability problem since there is no interaction between oil and shale, and the water can be made immobile using ionic solutions. (Chenevert, 1969). However, a solution for water-based mud (WBM) is needed especially in environmentally sensitive areas. Even though there have been many studies that focus on improving the hole stability properties of WBM, no such inhibited mud exists.